Air damper

ABSTRACT

An air damper includes: a piston adapted to reciprocate in a cylinder; an annular recessed portion formed along an outer periphery of the piston; a sealing member fitted in the recessed portion in a slidable manner, adapted to slidingly contact an inner peripheral surface of the cylinder, and forming air chambers on both sides of the piston, respectively, together with the piston; a communicating device allowing the air chambers formed on both sides of the piston to communicate with each other or not to communicate with each other depending on a stopping position of the sealing member; and a reduced-diameter portion formed by reducing a diameter of the cylinder on one end side thereof so as to gradually increase a frictional force between an inner periphery of the reduced-diameter portion and the sealing member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cylinder-type air damper in which airin air chambers formed in a cylinder is allowed to flow through anorifice as a piston moves relatively in the cylinder, so as to effectdamping.

2. Description of the Related Art

As an air damper of this type, for example, one for use in a glove boxof an automobile is known.

That is, an air damper is arranged such that an opening in a cylinder isclosed by a cap, and a piston rod penetrates the cap and extends outsidethe cylinder. The piston is provided with an O-ring, and the O-ring isfitted in an annular recess provided on an outer periphery of the pistonand abuts against the inner periphery of the cylinder. Two air chambersare respectively formed on both sides of the piston (a first air chamberis formed on the bottom side of the cylinder, and a second air chamberis formed on the opening side of the cylinder).

The piston is provided with an orifice allowing the first air chamber tocommunicate with the second air chamber.

The recess has such a width as to allow the O-ring to move along themoving direction of the piston. When the piston changes its movingdirection from the bottom of the cylinder toward the opening, the O-ringis moved from a second position to a first position by the frictionalforce between the O-ring and the inner periphery of the cylinder.Conversely, when the piston changes its moving direction from theopening toward the bottom, the O-ring is moved from the first positionto the second position by the aforementioned frictional force. A grooveis formed in the bottom of the recess, and when the O-ring is at thesecond position, the first air chamber and the second air chambercommunicate with each other through the groove, while when the O-ring isat the first position, the groove is blocked.

When the piston moves toward the opening side of the cylinder, the airflows by means of the orifice, and a damping force operates on the basisof the flow resistance at the orifice. On the other hand, when thepiston moves toward the bottom of the cylinder, the air escapes via thegroove, and the damping force is reduced.

In a case where such an air damper is used in a glove box, the pistonrod is connected to a lid of the glove box, and the cylinder isconnected to the accommodating side of the glove box. When the lid isopened, the piston rod is drawn out through the cylinder, so that thepiston moves from the bottom of the cylinder toward the opening.Consequently, when the lid is opened, the opening motion is made slow soas not to cause a shock. On the other hand, when the lid is closed, theclosing motion is becomes faster.

In a case where the lid of the glove box is opened from a vertical statetoward a horizontal state, the load applied to the lid becomes graduallygreater (the load changes) as the lid is opened, so that the lid-openingspeed becomes faster. Accordingly, as the lid approaches the position ofthis opening limit, the damping force caused by the air damper becomesinsufficient. At the position of the opening limit of the lid, the lidsometimes bounds, so that a smooth opening motion cannot be obtained.

Meanwhile, if the damping force of the air damper acts during an initialperiod of the opening motion of the lid, it is conceivable that the lidmay possibly remain in the vertical state and may not open.

SUMMARY OF THE INVENTION

In view of the above-described circumstances, it is an object of thepresent invention to provide an air damper for obtaining a satisfactorydamping by coping with a change in the load by changing the dampingforce.

To this end, in accordance with one aspect of the present invention,there is provided an air damper comprising: a piston adapted toreciprocate in a cylinder; an annular recessed portion formed along anouter periphery of the piston; a sealing member fitted in the recessedportion in a slidable manner, adapted to slidingly contact an innerperipheral surface of the cylinder, and forming air chambers on bothsides of the piston, respectively, together with the piston;communicating means allowing the air chambers formed on both sides ofthe piston to communicate with each other or not to communicate witheach other depending on a stopping position of the sealing member; and areduced-diameter portion formed by reducing a diameter of the cylinderon one end side thereof so as to gradually increase a frictional forcebetween an inner periphery of the reduced-diameter portion and thesealing member.

In the present invention, the piston reciprocates in the cylinder. Theannular recessed portion is formed on the outer periphery of the piston,and the sealing member is slidably fitted in the recessed portion. Thesealing member is adapted to slidingly contact the inner peripheralsurface of the cylinder, and together with the piston forms the airchambers on both sides of the piston, respectively.

Here, the piston is provided with the communicating means which allowsthe air chambers formed on both sides of the piston to communicate witheach other or not to communicate with each other depending on thestopping position of the sealing member which moves in the recessedportion, thereby causing the damping force to become effective orineffective.

In addition, as the piston moves toward one side of the cylinder, thefrictional force acting between the sealing member and the innerperipheral surface of the cylinder increases gradually due to thereduced-diameter portion of the cylinder. Hence, the air damper iscapable of exhibiting an appropriate damping force depending onfluctuations in the load acting on the piston.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view, taken in the direction of arrow A inFIG. 3, illustrating a state in which a piston is located at a first endof a cylinder of an air damper in accordance with a first embodiment ofthe present invention;

FIG. 2 is a diagram illustrating a state in which a piston is located ata second end of a cylinder, and corresponds to FIG. 1;

FIG. 3 is an exploded perspective view illustrating the air damper inaccordance with the first embodiment;

FIG. 4 is an enlarged cross-sectional view, taken in the direction ofarrow B in FIG. 3, of a portion of the air damper in accordance with thefirst embodiment, and illustrates a state in which the piston is locatedat a portion in the vicinity of the first end of the cylinder;

FIG. 5 is an enlarged cross-sectional view, taken in the direction ofarrow B in FIG. 3, of the portion of the air damper in accordance withthe first embodiment, and illustrates a state in which the piston islocated at a portion in the vicinity of the second end of the cylinder;

FIG. 6 is a diagram in which the air damper in accordance with thisfirst embodiment is applied to a glove box of an automobile;

FIG. 7 is a diagram illustrating a state of the air damper when a lid ofthe glove box is opened, and corresponds to FIG. 6;

FIG. 8 is a perspective view illustrating a glove box of an automobile;

FIG. 9 is a cross-sectional view, taken in the direction of arrow A inFIG. 11, of an air damper in accordance with a second embodiment of thepresent invention;

FIG. 10 is a diagram illustrating a state in which the piston is locatedat the second end of the cylinder, and corresponds to FIG. 9;

FIG. 11 is an exploded perspective view illustrating the air damper inaccordance with the second embodiment;

FIG. 12 is an enlarged cross-sectional view, taken in the direction ofarrow B in FIG. 11, of a portion of the air damper in accordance withthe second embodiment, and illustrates the state in which the piston islocated a portion in the vicinity of the second end of the cylinder;

FIG. 13 is an enlarged cross-sectional view, taken in the direction ofarrow B in FIG. 11, of the portion of the air damper in accordance withthe second embodiment, and illustrates the state in which the piston islocated a portion in the vicinity of the second end of the cylinder;

FIG. 14 is a cross-sectional view, taken in the axial direction of thecylinder, of a groove-forming portion;

FIG. 15 is a diagram illustrating a third embodiment, and corresponds toFIG. 9;

FIG. 16 is a diagram illustrating the third embodiment, and correspondsto FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 to 8, a description will be given of a firstembodiment of the air damper in accordance with the present inventionwhich is applied to a glove box of an automobile.

As shown in FIGS. 1 and 3, in an air damper 10, a piston 12 isreciprocatable in a cylinder 14 between one end, i.e., a first end (aleft end in FIG. 1) of the cylinder 14 and another end, i.e., a secondend (a right end in FIG. 1) along the axial direction (in theleft-and-right direction in FIG. 1) of the cylinder 14. The cylinder 14is comprised of a cylinder body 18, which has the shape of a hollowcylinder with a bottom and in which the first end is open and the secondend is a bottom 16, and a cap 20 for closing the open end, i.e. thefirst end. The cap 20 has the shape of a hollow cylinder with a bottom,and is fitted on the cylinder body 18 by allowing engaging throughholes22 provided in the peripheral portion of the cap 20 to engageresiliently to engaging projections 24 projecting from an outerperiphery of the cylinder body 18 in correspondence therewith. An O-ring26 is provided between the inner periphery of the cap 20 and the outerperiphery of the cylinder body 18 to provide airtightness for a firstair chamber 44 which will be described later. Incidentally, splitgrooves 28 are formed at the open end of the cap 20 to facilitate theengagement of the engaging projections 24 into the engaging holes 22.

As shown in FIGS. 4 and 5, the piston 12 is coaxial with the cylinder14, and has the shape of a hollow cylinder with a bottom, which is openon a side of the first end of the the cylinder 14 and has a bottom 30 ona side of the second end of the cylinder. One end of a piston rod 32 isconnected to the bottom 30 of the piston 12, The piston rod 32 has theshape of an elongated plate, and is positioned concentrically with thecylinder 14. Another end portion of the piston rod 32 penetrates througha through hole 34 (see FIG. 1) provided in the bottom 16 of the cylinder14, and extends outside the cylinder 14.

The outer periphery of the piston 12 is shaped such that large-diameterportions 36 and 38 are provided to form flanges which are spaced fromeach other at axial ends thereof, as shown in FIGS. 4 and 5, and anannular recess 40 is formed between the large-diameter portions, i.e.the second flanges, 36 and 38. An O-ring 42 which is formed of anelastic member serving as a sealing member and made of, for example, asynthetic resin such as a rubber, is fitted in the recess 40. In a statein which a gap is formed between the inner periphery of the cylinder 14and the outer peripheries of the large-diameter portions, i.e., thespaced flanges, 36 and 38, the O-ring 42 abuts against the innerperiphery of the cylinder 14, and the first air chamber 44 and a secondair chamber 46 are formed in the cylinder 14 on axially opposite sidesof the piston 12 (on both sides in the moving direction of the piston12). That is, the first air chamber 44 is formed on one end side of thecylinder 14, while the second air chamber 46 is formed on the other endside of the cylinder 14.

In addition, the bottom 30 of the piston 12 is provided with an orifice48 allowing the axially opposite sides of the piston 12 (the first airchamber 44 and the second air chamber 46) to communicate with eachother.

Meanwhile, in the recess 40, the O-ring 42 is movable along the axialdirection (in the widthwise direction of the recess 40) with respect tothe piston 12, and its moving range is set to be between a firstposition in the recess 40 (the position shown in FIG. 5) at which theO-ring is restricted by abutting against the large-diameter portion (theflange) 36 of the piston 12 on one end side thereof and a secondposition in the recess 40 (the position shown in FIGS. 1 and 4) at whichthe O-ring is restricted by abutting against the large-diameter portion(the flange) 38 of the cylinder 14 on the other end side thereof. Whenthe piston 12 changes its moving direction from the moving directionfrom the first end toward the second end of the cylinder 14 (indicatedby arrow C in the drawings) to the moving direction from the second endtoward the first end of the cylinder 1, the O-ring 42 moves from thefirst position toward the second position owing to the frictional forceacting between the O-ring 42 and the inner periphery of the cylinder 14.

On the other hand, when the piston 12 moves in the opposite direction,the O-ring 42 moves from the second position toward the first positionowing to the frictional force acting between the O-ring 42 and the innerperiphery of the cylinder 14.

In addition, portions of the large-diameter portion 38 are cut off alongthe widthwise direction of the recess 40 to form notches 50, and grooves52 which respectively communicate with the notches 50 are formed in thebottom of the recess 40. Each groove 52 extends to a widthwiseintermediate portion of the recess 40, and does not reach thelarge-diameter portion 36. When the O-ring 42 is at the second position,the O-ring 42 is located over the grooves 52, and a gap is formedbetween the inner peripheral surface of the O-ring 42 and the bottom ofeach groove 52. At this time, the second air chamber 46 and the firstair chamber 44 communicate with each other through the notches 50. Whenthe O-ring is at the first position, the O-ring is located in the recess40, so that the first air chamber 44 and the second air chamber 46 donot communicate with each other.

Incidentally, in this embodiment, two grooves 52 are formed in therecess 40.

In addition, as also shown in FIGS. 2 and 5, a reduced-diameter portion54 is formed at a portion in the vicinity of the second end of thecylinder 14. In this reduced-diameter portion 54, the inside diameter ofthe cylinder 14 is gradually reduced toward the second end of thecylinder 14, so that the inner periphery of the cylinder 14 is formed asa tapered surface toward the other second end thereof.

The O-ring 42 is in sliding contact with the inner periphery of thecylinder 14 as the piston 12 moves, so that a frictional force isgenerated between the O-ring 42 and the inner peripher of the cylinder14. When the piston moves through a portion which has the same diameter,not the reduced-diameter this frictional force on the O-ring is fixed,but when it is on the reduced-diameter portion 54, the frictional forceincreases as the piston 12 moves toward the second end of the cylinder14.

The opening/closing hole formed by each groove 52 is formed to be largerthan the diameter of the orifice 48. When the piston 12 moves toward thesecond end of the piston 14, the flow of air between the first airchamber 44 and the second air chamber 46 is effected by the orifice 48,and the damping force is increased to effect damping on the basis of theflow resistance of the air passing through the orifice 48.

On the other hand, when the piston 12 moves toward the first end of thecylinder 14, the flow of air between the first air chamber 44 and thesecond air chamber 46 is effected mainly by the grooves 52, and the airescapes through the grooves 52, thereby weakening the damping force todecrease the damping.

A mounting piece 56 is provided projectingly at one end portion of theouter periphery of the cylinder 14, and a mounting hole 58 is formed inthe mounting piece 56. In addition, a mounting hole 60 is formed at aprojecting tip of the piston rod 32.

In a glove box (although two vertically-arranged glove boxes 62 and 68are shown in FIG. 8, a description will be given of the upper glove box62) of an automobile in which the air damper 10 arranged as describedabove is used, as shown in FIGS. 6 and 7, a lid 64 serving as a movablemember of the glove box 62 is rotatably supported onto an accommodatingportion 66 of the glove box 62 by a rotating shaft 65 at a lower end ofthe lid 64, such that the lid 64 is closed in its vertical state (thestate shown in FIG. 6) and is opened in its horizontal state (the stateshown in FIG. 7).

The cylinder 14 is supported on the accommodating portion 66 side of theglove box 62 by means of the mounting hole 58 in the mounting piece 56,and is rotatable about the mounting hole 58. Meanwhile, the piston rod32 is supported by the lid 64 of the glove box 62 by means of themounting hole 60, and is rotatable about the mounting hole 60.

When the lid 64 is closed and is in the vertical state, the piston rod32 is retracted inside the cylinder 14, and the piston 12 is located atthe first end of the cylinder 14. As shown in FIG. 7, as the lid 64 inthe vertical state (indicated by the alternate long and short dash linein FIG. 7) is opened in the direction of arrow D, the piston rod 32 isextended from the cylinder 14, and the piston 12 moves in the cylinder14 from the first end toward the second end. In the horizontal position(indicated by the alternate long and two short dashes line in FIG. 7) inwhich the lid 64 has been completely opened, the piston 12 is located atthe second end of the cylinder 14.

In the above-described arrangement, as the piston 12 moves inside thecylinder 14, the air in the first air chamber 44 and the second airchamber 46 flows through the orifice 48, so that the damping is carriedout with respect to the opening and closing operation of the lid 64.

When the piston 12 moves, the O-ring 42 is in sliding contact with theinner periphery of the cylinder 14, and the frictional force actingbetween the O-ring 42 and the inner periphery of the cylinder 14 alsoimparts a damping force to the lid 64.

When the piston 12 moves from the first end toward the second end of thecylinder 14, and the O-ring 42 reaches the reduced-diameter portion 54of the cylinder 14, the frictional force acting between the O-ring 42and the inner periphery of the cylinder 14 thereafter increases as thepiston 12 moves toward the second end of the cylinder 14.

That is, as the lid 64 in its vertical state rotates and approaches itshorizontal state, the frictional force acting between the O-ring 42 andthe inner periphery of the cylinder 14 increases and the damping forceincreases, thereby making it possible to cope smoothly with fluctuationsin the load accompanying the opening of the lid 64. For this reason, thesmooth opening operation of the lid 64 can be achieved without boundingor the like at the position of an opening limit (horizontal position) ofthe lid 64.

In the reduced-diameter portion 54, the cone angle θ and the axiallength L of the reduced-diameter portion 54 shown in FIGS. 1 and 2 canbe set appropriately so as to be able to cope suitably with thefluctuations in the load.

In addition, the second end of the cylinder body 18 is formed as thebottom 16 and has the first end open, and the reduced-diameter portion54 is formed on the bottom 16 side of the cylinder body 18, so that theforming Of the reduced-diameter portion 54 in the cylinder 14 can befacilitated.

Further, if the air damper having the above-described arrangement isapplied to the so-called one-way type air damper in which the damping isincreased as the piston moves in one direction, while the damping isreduced as the piston moves in the opposite direction, the air damper iseffective in a case where when the lid 64 is opened, the opening motionis made slow, whereas when the lid 64 is closed, not much damping isrequired, or the closing motion is effected rather quickly.

Next, a description will be given of an air damper 110 in accordancewith a second embodiment. It should be noted that portions or partswhich are identical to those of the first embodiment will be denoted bythe same reference numerals, and a description thereof will be omitted.

As shown in FIGS. 10 and 12, a groove-forming portion 154 is formed at afirst end portion of the cylinder 14 constituting the air damper 110. Inthe groove-forming portion 154, grooves 155 are formed on the innerperiphery of the cylinder 14. These grooves 155 are recessed such thatthe diameter of an imaginary circle formed by extending the bottoms ofthe grooves 155 is larger than the inside diameter of the cylinder 14.The grooves 155 extend from the first end of the cylinder 14 along theaxial direction, and four grooves 155 are formed at 90° intervals in thecircumferential direction, as shown in FIG. 14. In a case where theO-ring 42 is located in an intermediate portion of the groove-formingportion 154 in its longitudinal direction, each groove 155 forms a gapwith respect to the O-ring 42, a first side thereof communicates withthe first air chamber 44, while a second side thereof communicates withthe second air chamber 46. The combined cross-sectional areas of thegrooves 155 are formed to be larger than the cross-sectional area of theorifice 48.

Accordingly, when the piston 12 moves from the first end toward secondend of the cylinder 14, the O-ring 42 is located at the groove-formingportion 154 at the portion in the vicinity of the first end of thecylinder 14, and air escapes through the grooves 155, thereby weakeningthe damping force to decrease the damping. After the O-ring 42 has leftthe groove-forming portion 154, as the piston 12 moves toward the secondend of the cylinder 14, the damping becomes effective on the basis ofthe orifice 48.

For this reason, during an early period of the movement of the lid 66when the load acting on the piston 12 is small, it is possible toeffectively obtain a free moving state which does not exert a dampingforce, thereby making it possible to cope with fluctuations in the loadaccompanying the opening of the lid 66.

It should be noted that, as for the groove-forming portion 154, theaxial length L (see FIGS. 9 and 10) of the groove-forming portion 154,the number of the grooves 155, the shape and the size of each groove155, and the like are set appropriately so as to cope suitably with thefluctuations in the load.

As for the grooves 155, it is sufficient if the diameter of theimaginary circle formed by extending the bottoms of the grooves 155 islarger than the inside diameter of the cylinder 14. Although, in theabove-described embodiment, the grooves 155 are elongated, the width(circumferential dimension) of each groove 155 may not be narrow, as inthe above-described embodiment, but wide, and is not limited to aparticular width.

Further, the cylinder 1 has the shape of a hollow cylinder with a bottomthe second end of which is formed as the bottom 16, and the first end ofwhich is open, and the groove-forming portion 154 is formed on the openend side of the cylinder 14. Since the diameter of the imaginary circleformed by extending the bottoms of the grooves 155 of the groove-formingportion 154 is made larger than the inside diameter of the cylinder 14,the forming of the groove-forming portion 154 in the cylinder 14 isfacilitated.

As the piston 12 moves, the O-ring 42 slidingly contacts the innerperiphery of the cylinder 14, and a frictional force is produced betweenthe O-ring 42 and the inner periphery of the cylinder 14. Since thegrooves 155 are recessed such that the diameter of the imaginary circleformed by extending the bottoms of the grooves 155 is larger than theinside diameter of the cylinder 14, the O-ring 42 is not brought intocontact with the grooves 155 in the groove-forming portion 154, so thatthe contact pressure does not increase. Instead of forming the grooves155, it is conceivable to provide ribs projecting inwardly from theinner periphery of the cylinder 14. In this case, however, the ribs biteinto the O-ring, so that the resistance becomes large. Stillalternatively, instead of forming the grooves 155, it is conceivable toform a cone surface on the inner periphery of the cylinder 14 bygradually enlarging the inside diameter of the cylinder 14 on theportion in the vicinity of the first end thereof. In this case, however,there is a zone in which the cone surface and the O-ring fail to contacteach other depending on the position of the piston 12, so that aclearance is formed between the piston 12 and the inner periphery of thecylinder 14. As a result, the piston rod moves in an undulating mannerand becomes unstable.

Referring now to FIGS. 15 and 16, a description will be given of a thirdembodiment.

In the above-described second embodiment, the groove-forming portion 154is formed in the portion in the vicinity of the first end of thecylinder 14. In an air damper 111 of this embodiment, however, agroove-forming portion 102 is formed not only the portion in thevicinity of the first end portion of the cylinder 14 but also at aportion excluding the portion in the vicinity of the second end of acylinder body 106 of a cylinder 104 in such a manner as to extend fromone end of the cylinder 104. In addition, the orifice 48 similar to theone in the second embodiment is used as a first orifice, and grooves 108in the groove-forming portion 102 are used as second orifices.

In accordance with this arrangement, at a time when the piston 12 movesfrom the first end toward the second end of the cylinder 104, when theO-ring 42 is at the groove-forming portion 102, air flow takes placethrough the orifice 48 and the grooves 108, so that the damping force isweakened due to the orifices 48 and 108, thereby reducing the damping.

Meanwhile, when the O-ring 42 leaves the groove-forming portion 102 andreaches the second end portion of the cylinder 14, air does not flow inthe grooves 108, and air flow takes place only by the orifice 48, sothat the damping becomes effective, thereby making it possible to copewith fluctuations in the load.

Incidentally, as for the groove-forming portion 102, the axial length Lof the groove-forming portion 102, the number of the grooves 108, theshape of each groove 108, and the like are set as required so as to copesuitably with the fluctuations in the load, in the same way as in theabove-described first embodiment. The other arrangements and advantagesin operation are similar those of the second embodiment.

Although in the foregoing embodiments a description has been given of acase in which the air damper is applied to a glove box of an automobile,the present invention is not limited to the same. For instance, the airdamper in accordance with the present invention is applicable to otheritems such as an opening/closing cover of an operation panel of atelevision set or the like.

In addition, although in the above-described embodiments a lid servingas a movable member is connected to the piston side, the lid may beconversely connected to the cylinder side.

As described above, in accordance with the air damper of the presentinvention, it is possible to cope with fluctuations in the load byvarying the damping force, thereby obtaining a suitable damping.

What is claimed is:
 1. An air damper comprising;a cylinder: a pistonadapted to reciprocate in said cylinder; an annular recessed portionformed along an outer periphery of said piston; a sealing memberslidably movable in said annular recessed portion between at least twopositions, said sealing member slidingly contacting an inner peripheralsurface of said cylinder, said sealing member and said pistoncooperating to form air chambers on both sides of said piston;communicating means allowing said air chambers formed on both sides ofsaid piston to communicate with each other or not to communicate witheach other depending on the position of said sealing member in saidrecess; said cylinder having a portion of reduced interior diameter inthe vicinity of one end of said cylinder, said portion graduallydecreasing in interior diameter toward said one end to graduallyincrease frictional force between said portion of reduced interiordiameter and said sealing member in order to provide a graduallyincreasing damping effect.
 2. An air damper according to claim 1,wherein said cylinder is a hollow cylindrical member with a bottom, oneend of said cylinder being open, said open end being hermetically closedby a cap, said bottom being provided with a through hole through which apiston rod connected to said piston is passed through.
 3. An air damperaccording to claim 2, wherein said cap is provided with an engaging holein which a projection on an outer periphery of said cylinder in avicinity of said opening is capable of engaging.
 4. An air damperaccording to claim 2, wherein said reduced-diameter portion is providedon a bottom side of said hollow cylindrical member.
 5. An air damperaccording to claim 2, wherein an O-ring is provided between engagingsurfaces of said cap and said hollow cylindrical member.
 6. An airdamper according to claim 1, wherein said piston has a piston rod, andsaid piston is provided with an orifice penetrating said piston.
 7. Anair damper according to claim 6, wherein a diameter of said orifice issmaller than a communicating hole formed by said communicating means. 8.An air damper according to claim 1, wherein said sealing member is anO-ring.
 9. An air damper comprising:a cylinder; a piston adapted toreciprocate in said cylinder; said piston having spaced flanges on anouter periphery thereof defining therebetween an annular recessedportion; a sealing member slidably movable in said annular recessedportion between at least first and second positions, said sealing memberslidingly contacting an inner peripheral surface of said cylinder, saidsealing member and said piston cooperating to form air chambers on bothsides of said piston; communicating means comprising a notched portionin one of said flanges, and a groove in a bottom of said annularrecessed portion extending from a predetermined position in said annularrecessed portion to said notched portion to communicate or not tocommunicate with said air chamber formed on both sides of said pistondepending on the position of said sealing member in said recess; saidcylinder having a portion of reduced interior diameter in the vicinityof one end of said cylinder, said portion gradually decreasing ininterior diameter toward said one end to gradually increase frictionalforce between said portion of reduced interior diameter and said sealingmember in order to obtain a gradually increasing damping effect.
 10. Anair damper according to claim 9, wherein said first position is adjacentone of said spaced flanges and said second position is adjacent anotherof said spaced flanges, and wherein said sealing member is movabletherebetween.